KR101552409B1 - Image forming apparatus - Google Patents

Abstract

The temperature of the print medium 110 is sufficiently lowered by stopping the print medium 110 in the discharge path, conveying the print medium at a low speed, or switching the conveying path. If the temperature of the print medium 110 can be sufficiently lowered, the thermochromism phenomenon is suppressed. Accordingly, it is possible to provide an image forming apparatus capable of realizing highly accurate color matching and color stability.

Description

[0001] IMAGE FORMING APPARATUS [0002]

The present invention relates to an image forming apparatus having a colorimetric value measurement function.

The image quality of the image forming apparatus includes granularity of one page, in-plane homogeneity of the image, character quality, color reproducibility (including color stability), and the like. Nowadays, in which multicolor image forming apparatuses have become widespread, the most important image quality is sometimes referred to as color reproducibility. Humans have memories of the color they expect based on their experience (especially human skin, blue sky, metal, etc.), and feel the sense of incongruity when the color exceeds the acceptable range. These colors are referred to as memory colors and their reproducibility becomes more important when outputting photographs. Among office users who feel a sense of incongruity due to the color difference of the monitor and users in the graphic art field seeking color reproducibility of the CG image, not only the photographic image but also the document image, the color (including stability) reproducibility Needs are increasing.

Japanese Patent Application Laid-Open No. 2004-086013 proposes an image forming apparatus that reads a patch image (measurement image) formed on a print medium by a color sensor provided in a print medium conveyance path to satisfy a user's demand for color reproducibility . The invention described in Japanese Patent Application Laid-Open No. 2004-086013 has an advantage that an ICC profile can be automatically generated as compared with an offline colorimetric value measuring apparatus that reads a patch image of a print medium discharged to the outside by the image forming apparatus . "ICC" stands for International Color Consortium. The color management module (CMM) performs color conversion using the ICC profile, thereby realizing color matching between a plurality of image forming apparatuses or between the image forming apparatus and the image display apparatus.

However, according to the invention of Japanese Patent Laid-Open Publication No. 2004-086013, since the color sensor is disposed on the conveying path in the vicinity of the fixing device, a so-called "thermochromism ", in which the chromaticity of the measurement image, ) "The phenomenon becomes a problem. This is a phenomenon that the molecular structure forming the coloring material such as toner or ink changes due to "heat" or the like.

In order to measure the colorimetric value of the measurement image in the image forming apparatus, the apparatus needs to be in a state in which color mixing is completed after the coloring material is placed on the print medium. In an image forming apparatus using an ink as a coloring material, it is necessary to measure the colorimetric value after drying the ink by a dryer. In the image forming apparatus using the toner as the coloring material, it is necessary to measure the colorimetric value after mixing and coloring the toner by heating and fusing with the fixing device. This is because a user who requires color matching accuracy or color stability generally judges based on the image of the room temperature environment. Therefore, the color sensor needs to be disposed in the sheet conveying direction on the downstream side of the dryer or the fixing device.

On the other hand, in order to make the image forming apparatus compact, it is necessary to set the length of the conveying path from the dryer or the fixing device to the color sensor to the minimum length. Therefore, the sheet and the coloring material heated by the dryer or the fixing device are not cooled to room temperature, but are conveyed to the color sensor. Further, the temperature of the printing medium is higher than the room temperature even by the temperature rise of the internal components of the image forming apparatus such as the printing medium conveying guide.

As described above, in some cases, the image forming apparatus provided with the color sensor has a colorimetric measurement result different from the colorimetry in a normal environment (room temperature environment) due to the influence of the thermochromism do. The reproducibility standard, which is a standard of stability according to ISO 12647-7, and the color matching accuracy standard, which are indicators of color matching accuracy and color stability, may not be satisfied.

The present invention provides an image forming apparatus capable of suppressing a chromatic phenomenon in which the chromaticity of an image for measurement changes due to temperature, and achieving highly accurate color matching and color stability.

The present invention provides an image forming apparatus, comprising: image forming means for forming an image on a printing medium by using a color material; fixing means for fixing the image to the printing medium; A colorimetric value measuring means for measuring a colorimetric value of an image fixed on the printing medium at a downstream side of the fixing means; and a colorimetric value measuring means for measuring the colorimetric value of the image fixed on the printing medium, The time from when the colorimetric value is measured by the colorimetric value measurement means until the colorimetric value is measured by the colorimetric value measurement means is measured by the colorimetric value measurement means from the fixing means when the colorimetric value measurement is not performed by the colorimetric value measurement means And a control means for setting a time longer than a time taken for the transfer to be carried out by the means.

According to the present invention, the temperature of the printing medium is sufficiently lowered by stopping the printing medium in the discharge path, conveying the printing medium at a low speed, or switching the conveying path. If the temperature of the printing medium can be sufficiently lowered, the thermochromism phenomenon is suppressed. Accordingly, it is possible to provide an image forming apparatus capable of realizing highly accurate color matching and color stability.

Other aspects of the invention will become apparent by reference to the following description of an exemplary embodiment (together with the accompanying drawings).

1 is a view showing an image forming apparatus.
2 is a view showing a color sensor.
3 is a view showing a control block.
4 is a diagram showing an ICC profile.
5 is a diagram showing a color management environment.
Fig. 6 is a flowchart showing Embodiment 1. Fig.
Figs. 7A to 7C are diagrams showing standby positions in Embodiment 1. Fig.
8 is a graph showing the relationship between the print medium standby time, the print medium surface temperature, and? E76 (comparison with 15 占 폚).
9 is a diagram showing a possible range of the print medium temperature in the image forming apparatus.
10 is a diagram showing an example of the cooling time for each print medium type.
11A and 11B are diagrams showing the buffer of the second embodiment.
12 is a flowchart showing Embodiment 2;
13 is a diagram showing the relationship between the print medium standby time, the paper surface temperature, and? E76 (comparison with 15 占 폚).
14 is a block diagram showing the system configuration of the image forming apparatus.
Fig. 15 is a graph showing a tendency of chromaticity change for each coloring material.
FIG. 16 is a graph showing the tendency of density change for each coloring material.
17A to 17C are diagrams showing spectral reflectance data at respective temperatures when colorimetric values of a magenta patch image are measured by a color sensor.
18A and 18B are diagrams showing filter sensitivity characteristics used in density calculation processing.
19 is a flowchart showing the operation of the image forming apparatus.
20 is a flowchart showing the maximum density adjustment operation.
21 is a flow chart showing the tone adjustment operation.
22 is a flowchart showing the multicolor correction processing operation.
23 is a flowchart showing a target value calculation processing operation.
24 is a table showing a comparison of the effects of the embodiment and the comparative example.
25 is a flowchart showing the operation of the image forming apparatus.
26 is a flowchart showing multicolor correction processing.
27A and 27B are views showing a print medium setting screen.
28 is a diagram showing the fixing conditions for each mode.
29 is a view showing a mode for combination of basis weight and glossiness of recycled paper.
30 is a view showing a mode for combination of basis weight and gloss of high quality paper.
31 is a view showing a mode for combination of basis weight and glossiness of coated paper.
32 is a view showing a mode for combination of basis weight and glossiness of recycled paper.
33 is a diagram showing a mode for combination of basis weight and gloss of high quality paper.
34 is a diagram showing a mode for combination of basis weight and gloss of a coated paper.

In the present invention, the time from the passage of the print medium through the fixing unit when the colorimetric value measurement is performed by the colorimetric value measurement unit to the time when the colorimetric value measurement is performed by the colorimetric value measurement unit, Is longer than the time taken for the print medium to be transported from the fusing unit to the colorimetric value measurement unit. Particularly, Embodiment 1 is characterized by controlling the conveying speed of the printing medium in the conveying path (temporarily setting the conveying speed to zero). The second embodiment is characterized in that the conveying distance is set longer by switching the conveying path. It should be noted that in Embodiment 2, when a sufficient conveying distance can not be secured even when the conveying path is switched, the conveying speed may be lowered in some conveying paths. Both of the embodiments are characterized in that the print medium reaches the colorimetric value measurement unit after a predetermined time has elapsed from the point at which the print medium passes the fusing unit by controlling the conveying path or the conveying speed. Here, the predetermined time is a time at which the color difference? E76 obtained by the colorimetric value measurement unit at the temperature of the environment in which the image forming apparatus is installed is 1.5 or less. That is, the predetermined time is a time at which the temperature of the print medium reaching the colorimetric value measurement unit decreases to 45 占 폚 or less. Therefore, in the present invention, the temperature of the printing medium is sufficiently lowered by stopping the printing medium in the discharge path, conveying the printing medium at a low speed, or switching the conveying path. If the temperature of the printing medium can be sufficiently lowered, the thermochromism phenomenon is suppressed. As a result, it is possible to provide an image forming apparatus capable of realizing highly accurate color matching and color stability.

[Example 1]

(Image forming apparatus)

In this embodiment, a solution to the above-mentioned problem will be described using an electrophotographic laser beam printer. Here, for example, an electrophotographic system is adopted as an example of an image forming system. However, the present invention can also be applied to ink jet printers and sublimation printers. The reason for this is that the present invention is effective for an image forming apparatus in which the chromaticity of the object to be measured can cause a thermochromic phenomenon that changes due to temperature. It should be noted that in an ink jet printer, an image forming unit for discharging ink to form an image on a printing medium and a fixing unit (drying unit) for drying the ink are used.

1 is a sectional view showing a structure of an image forming apparatus 100. As shown in Fig. The image forming apparatus 100 has a housing 101. The housing 101 is provided with mechanisms constituting an engine section and a control board housing section 104. The control board housing section 104 houses an engine control section 102 and a printer controller 103 that perform control relating to print processing (for example, paper feeding processing) performed by the respective mechanisms.

As shown in Fig. 1, the engine unit has four stations 120, 121, 122, and 123 corresponding to YMCK. The stations 120, 121, 122, and 123 are image forming units that transfer the toner onto a print medium to form an image. Here, "YMCK" is an abbreviation of yellow, magenta, cyan, and black. Each station is composed of substantially common components. The photosensitive drum 105 is an image bearing member and is charged to a uniform surface potential by the primary charging device 111. [ A latent image is formed on the photosensitive drum 105 by the laser light output by the laser 108. [ The developing device 112 develops the latent image using a color material (toner), and forms a toner image. The toner image (visible image) is primarily transferred to the intermediate transfer member 106. The visible image formed on the intermediate transfer member 106 is secondarily transferred to the transfer roller 114 with respect to the print medium 110 conveyed from the container 113. [

The fixing mechanism of this embodiment has a first fixing device 150 and a second fixing device 160 for heating and pressurizing the toner image transferred to the printing medium 110 to fix the toner image on the printing medium 110 have. The first fixing device 150 includes a fixing roller 151 for applying heat to the printing medium 110, a pressing belt 152 for pressing the printing medium 110 against the fixing roller 151, And a sensor 153 after the fixation. These rollers are hollow rollers and have a heater inside. These rollers are driven by a motor not shown in the drawing, and convey the print medium 110. The second fixing device 160 is disposed on the downstream side of the first fixing device 150 in the conveying direction of the printing medium 110. The second fixing device 160 adds gloss to the toner image of the print medium 110 fixed by the first fixing device 150 and maintains fixability. Similar to the first fixing device 150, the second fixing device 160 also has a fixing roller 161, a pressing roller 162, and a second fixing sensor 163. Some types of print media 110 need not pass through the second fusing device 160. In this case, for the purpose of reducing energy consumption, the print medium 110 passes through the conveyance path 130 without passing through the second fixing device 160. For example, when a large amount of heat is required for fixation, such as when the image of the print medium 110 is set to add a lot of gloss to the image, or when the print medium 110 is thick paper, the first fixation device 150 Is conveyed to the second fixing device 160 as well. On the other hand, if the print medium 110 is not set to be plain paper or a thin paper or a lot of gloss, the print medium 110 is conveyed to the conveyance path 130 bypassing the second fixing device 160. Whether the print medium 110 is conveyed to the second fixing device 160 or the printing medium 110 is conveyed by bypassing the second fixing device 160 is controlled by switching the switching member 131.

The switching member 132 performs switching to guide the print medium 110 to the discharge path 135 or to guide the print medium 110 to the external discharge path 139. [ An inversion sensor 137 is provided in the discharge path 135. The leading end of the print medium 110 passes through the reversing sensor 137 and is conveyed to the reversing portion 136. [ When the reversing sensor 137 detects the rear end of the print medium 110, the conveying direction of the print medium 110 is switched. The switching member 133 conducts switching to lead the print medium 110 to the conveyance path 138 for forming the double-side image, or to guide it to the discharge path 135. [ The switching member 134 guides the print medium 110 to the external discharge path 139.

A color sensor 200 for detecting a measurement image (hereinafter referred to as a "patch image") of the print medium 110 is disposed on the downstream side of the second fixing device 160 in the conveying direction of the print medium 110 . Four color sensors 200 are arranged side by side in a direction orthogonal to the conveying direction of the printing medium 110 and four rows of patch images can be detected. Therefore, a plurality of color sensors 200 can be provided. When color detection is instructed by the operation unit 180, the engine control unit 102 performs density adjustment, gradation adjustment, multicolor adjustment, and the like.

The density sensor 170 serving as the density detecting unit is provided so as to be opposed to the intermediate transfer member 106. The density sensor 170 is a regular reflection type sensor having a light emitting element 171 and a light receiving element 172 constituted by light emitting diodes (LEDs). In the present embodiment, the mirror-type sensor is used, but the sensor is not limited thereto. Alternatively, the sensor may be a diffusely reflective sensor or a sensor using a combination of the mirror-reflection type and the mirror-reflection type.

(Color sensor)

2 is a view showing the structure of the color sensor 200. As shown in Fig. A white LED 201, a diffraction grating 202, a line sensor 203, an arithmetic unit 204, and a memory 205 are provided inside the color sensor 200. The white LED 201 is a light emitting element that emits light to the patch image 220 of the print medium 110. The diffraction grating 202 is a spectroscopic component that spectrums the light reflected from the patch image 220 by wavelength. The line sensor 203 is a photodetecting element including n light receiving elements for detecting light that has been wavelength-dispersed by the diffraction grating 202. The arithmetic unit 204 performs various arithmetic operations from the luminosity values of the respective pixels detected by the line sensor 203. [ The memory 205 stores various data used by the arithmetic operation unit 204. [ The arithmetic unit 204 has, for example, a spectral calculation unit for performing spectral calculation from a luminance value and a Lab calculation unit for calculating an Lab value. The lens 206 for condensing the light irradiated from the white LED 201 onto the patch image 220 of the print medium 110 and for condensing the light reflected from the patch image 220 onto the diffraction grating 202 May be installed.

(profile)

The image forming apparatus 100 generates a profile from the patch image detection result, and converts the input image using this profile to form an output image. As a profile for realizing excellent color reproducibility, here, an ICC profile which is accepted in the market is used. However, the present invention is not an invention that can be applied only to the ICC profile. The present invention can be applied to CMYK simulation in ColorWise of EFI company which maintains information on CRD (Color Rendering Dictionary), color decomposition table in Photoshop, and inking plate information adopted from PostScript level 2 by Adobe.

The user operates the operating section 180 to instruct the color profile generation processing to perform color profile generation processing before performing a job requiring color matching accuracy at the time of part replacement by a maintenance technician or when the user wants to know the color of the final output at the design stage do.

The profile creation processing is performed by the printer controller 103 shown in the block diagram of Fig. The printer controller 103 having a CPU reads a program for executing a flowchart to be described later from the storage unit 350 and executes the program. In Fig. 3, the inside of the printer controller 103 is represented by a block in order to facilitate understanding of the process performed by the printer controller 103. Fig. When the operation unit 180 receives the profile creation instruction, the profile generation unit 301 outputs the CMYK color chart, ISO12642 test form, to the engine control unit 102 without a profile. The profile generation unit 301 transmits the colorimetric value measurement instruction to the color sensor control unit 302. [ The engine control unit 102 controls the image forming apparatus 100 to cause the image forming apparatus 100 to execute processes such as charging, exposure, development, transfer, and fixation. Accordingly, the ISO 12642 test form is formed on the print medium 110. [ The color sensor control unit 302 controls the color sensor 200 to allow the color sensor 200 to measure the colorimetric value of the ISO 12642 test format. The color sensor 200 outputs the spectral reflectance data as a result of the colorimetric value measurement to the Lab operation unit 303 of the printer controller 103. The Lab computing unit 303 converts the spectral reflectance data into L * a * b * data and outputs L * a * b * data to the color sensor input ICC profile storage unit 304. [ The color sensor input ICC profile storage unit 304 converts the L * a * b * data input from the Lab operation unit 303 according to the color sensor input ICC profile and outputs the changed L * a * b * data to the profile generation unit 301. It should be noted that the Lab operation unit 303 can convert the spectral reflectance data into the CIE1931XYZ color space, which is a device-independent color space signal. The color sensor input ICC profile stored in the color sensor input ICC profile storage unit 304 is composed of a plurality of LUTs (lookup tables). This LUT is, for example, a one-dimensional LUT for controlling the gamma of the input signal, a multicolor LUT called "direct mapping ", and a one-dimensional LUT for controlling the gamma of the generated transformed data.

The profile generation unit 301 generates an output ICC profile based on the relationship between the CMYK color signal output to the engine control unit 102 and the L * a * b * data input by the Lab operation unit 303. [ The profile generation unit 301 stores the generated output ICC profile instead of the output ICC profile stored in the output ICC profile storage unit 305. [

The ISO 12642 test form includes a patch of a CMYK color signal covering a color reproduction area that can be output by a general copier. Therefore, the profile generation unit 301 generates the color conversion table based on the relationship between the L * a * b * values obtained by measuring the color signal value and the colorimetric value. That is, the CMYK? Lab conversion table is generated. An inverse transformation table is generated based on this conversion table.

Fig. 4 shows the data structure of the ICC profile. The ICC profile includes a header, a tag and its data. The tag includes a color conversion table tag, a white point (wtpt), and a tag (gamt) describing whether the color represented by the Lab value defined in the profile is inside or outside the reproducible range.

Upon receiving a profile creation command from the host computer via the I / F 308, the profile creation unit 301 outputs the generated output ICC profile to the host computer via the I / F 308. [ The host computer can implement the color conversion corresponding to the ICC profile in the application program.

(Color conversion processing)

In the color conversion for a normal color output, an image signal inputted by assuming a RGB image signal input through the I / F 308 from the scanner unit or a standard print CMYK signal value such as JapanColor is stored as an input ICC profile for external input (307). The input ICC profile storage unit 307 performs RGB → L * a * b * or CMYK → L * a * b * conversion in accordance with the image signal input from the I / F 308. The input ICC profile stored in the input ICC profile storage unit 307 is composed of a plurality of LUTs (lookup tables). This LUT is, for example, a one-dimensional LUT for controlling the gamma of the input signal, a multicolor LUT called "direct mapping ", and a one-dimensional LUT for controlling the gamma of the generated transformed data. The input image signal is converted into L * a * b * data that does not depend on the device from the device-dependent color space using this LUT.

The image signal converted into the L * a * b * chromaticity coordinates is input to the CMM 306. [ "CMM" is an abbreviation of color management module. The CMM 306 performs various color conversion. For example, the CMM 306 performs a GUMAT conversion for mapping a discrepancy between a read color space such as a scanner unit serving as an input device and an output color reproduction range of the image forming apparatus 100 serving as an output device do. In addition, the CMM 306 performs color conversion to adjust the mismatch between the light source type at the time of input and the type of light source used for observing the output (also referred to as "mismatch of color temperature setting"). Accordingly, the CMM 306 converts L * a * b * data into L '* a' * b '* data and outputs L' * a '* b' * data to the output ICC profile storage unit 305 Output. The profile generated as a result of the colorimetric value measurement is stored in the output ICC profile storage unit 305. Therefore, the output ICC profile storage unit 305 carries out color conversion on L '* a' * b '* data based on the newly generated ICC profile, converts it into a CMYK signal dependent on the output device, And outputs a signal to the engine control unit 102.

3, the CMM 306 is separate from the input ICC profile storage unit 307 and the output ICC profile storage unit 305. [ However, as shown in FIG. 5, the CMM 306 is a module responsible for color management and performs color conversion using an input profile (print ICC profile 501) and an output profile (printer ICC profile 502) Conduct.

(Control flow)

Control of printing medium conveyance and colorimetric value measurement, which is a feature of this embodiment, will be described with reference to the flowchart of FIG. 6 and the print medium position explanatory diagram of FIG.

In step S601, the printer controller 103 receives print medium information indicating the print medium type (thickness, grammage (basis weight), surface property, etc.) through the operation unit 180. [ When a sensor for detecting the type of print medium is installed in the conveyance path, the printer controller 103 can acquire the print medium information from this sensor.

In step S602, the printer controller 103 starts a color adjustment mode for performing color adjustment. The start instruction can also be received by the operation unit 180. [

In step S603, the printer controller 103 instructs the engine control unit 102 to feed the print medium 110. [ The engine control unit 102 starts the conveying roller driving motor 311 to feed the printing medium 110 from the container 113 to the conveying path.

In step S604, the printer controller 103 instructs the engine control unit 102 to control each station so that the intermediate transfer member 106 transfers the test pattern. Further, the printer controller 103 transmits the print medium information to the engine control unit 102. [ Based on the print medium information, the engine control unit 102 secondarily transfers the test pattern from the intermediate transfer member 106 to the print medium 110 by using the transfer condition according to the print medium type.

As a result of the printer controller 103 transmitting the print medium information to the engine control unit 102 in step S605, the engine control unit 102 controls the first fixing device 150 and the second fixing device 150, 2 The fixing device 160 is controlled, and the test form is fixed on the print medium 110. The engine control unit 102 controls the switching member driving motor 312 that drives the switching member 131 in accordance with the type of printing medium so that the printing medium 110 passes through only the first fixing device 150, Allowing both the device 150 and the second fusing device 160 to pass through. For example, in the case of plain paper, the engine control unit 102 allows the printing medium 110 to pass through only the first fixing device 150, and in the case of the paper or coated paper, the printing medium is conveyed only by the first fixing device 150 But also the second fixing device 160.

If the printer controller 103 detects in step S606 that the leading end of the printing medium 110 has passed through the first post-fixing sensor 153 or the second post-fixing sensor 163 through the engine control unit 102, The timer 310 in the engine control unit 102 starts the time measurement. Here, in this embodiment, the time required to lower the temperature of the print medium 110 to the environmental temperature is referred to as "predetermined time T ". For example, the predetermined time T is a time at which the chrominance? E76 becomes less than 1.5 after the timer 310 starts counting. In this embodiment, the colorimetric measurement accuracy target value of the color sensor 200 is defined as DELTA E76 = 1.5 in consideration of the individual difference of the color sensor 200 and the repeated readability of the same color patch.

Magenta has been found experimentally that the change in chromaticity due to temperature is greater than that of other colors. Particularly, because of the relationship between the conveyance time, the print medium temperature, and the magenta color difference? E, the predetermined time T is set to about 45 seconds in the present embodiment. Figs. 7A to 7C are diagrams showing positions where the print medium 110 is waiting for a predetermined time T in the image forming apparatus 100. Fig.

In step S607, the printer controller 103 causes the engine control unit 102 to continue the conveyance of the print medium 110, and as a result, the front end of the print medium 110 as shown in Fig. 200). It should be noted that the printer controller 103 does not start the colorimetric value measurement at this time.

In step S608, the printer controller 103 causes the engine control unit 102 to further carry the carriage of the print medium 110. [ 7B, when the reversal sensor 137 detects that the print medium 110 has reached the inverting unit 136, the printer controller 103 controls the operation of the print medium 110 via the engine control unit 102, Stop the transportation. That is, the engine control unit 102 stops the conveying roller driving motor 311. Thereby, the print medium 110 waits at the inverting unit 136. [

In step S609, the printer controller 103 determines whether or not the type indicated by the print medium information requires a cooling time. For example, the printer controller 103 has a table indicating whether or not the cooling time is required for each print medium information. This table is stored in the storage unit 350, for example. The printer controller 103 refers to this table to determine whether or not it is a type requiring a cooling time. It is determined whether or not it is necessary to wait the print medium 110 in the inverting unit 136 and whether or not the conveying speed of the print medium 110 is lowered at the inverting unit 136 Is substantially the same as whether or not it is necessary to determine whether or not there is a need to Therefore, this table is used to determine whether or not the print medium information and the corresponding conveyance path (whether or not the inversion to the reversing unit 136 is necessary) or the conveyance speed (whether or not the reversing unit 136 needs to wait for the paper) This is an example of a table associated with each other. As described above, the printer controller 103 acquires the conveyance path or conveyance speed corresponding to the print medium information received by the operation unit 180 from the table, and uses the obtained conveyance path or conveyance speed. If a cooling time is required, the process proceeds to step S610. If no cooling time is required, the process skips steps S610 to S612 and proceeds to step S613.

In step S610, the printer controller 103 acquires the timer value from the timer 310 and determines whether or not the timer value exceeds the predetermined time T. [ If the timer value exceeds the predetermined time T, the process proceeds to step S611.

In step S611, the printer controller 103 causes the engine control unit 102 to reset the timer 310. [

In step S612, the printer controller 103 causes the engine control unit 102 to resume conveyance of the print medium 110. [ The engine control unit 102 resumes the driving of the conveying roller driving motor 311 to direct the printing medium 110 to the color sensor 200. [

The printer controller 103 causes the engine control unit 102 to continue the conveyance of the print medium 110 in step S613. As a result, the print medium 110 is conveyed to the color sensor 200, .

According to the present invention, the predetermined time (T) has elapsed at the time when the print medium (110) reaches the color sensor (200). Therefore, the colorimetric measurement accuracy depending on the thermochromism at this point is? E76 = 0.5 or less. Strictly speaking, at this point in time, a time longer than a predetermined time T has elapsed. This is because, after the carriage of the print medium 110 is resumed in step S612, the time required for the print medium 110 to reach the color sensor 200 has elapsed. Since this time is several seconds, it does not affect the accuracy of the colorimetric measurement.

In step S614, the printer controller 103 causes the color sensor 200 to measure the colorimetric value through the color sensor control unit 302. [ The print medium 110 whose colorimetric value measurement by the color sensor 200 has been completed is discharged to the outside of the image forming apparatus 100 along the discharge path 139 as shown in Fig.

(Explanation of effect)

As described above, according to the present invention, the temperature of the print medium 110 can be lowered to a temperature suitable for the colorimetric value measurement by waiting the print medium 110 for a predetermined time according to the type of the print medium 110 .

8 shows the relationship between the waiting time of the printing medium 110, the temperature, and the position in the conveying path of? E76 (comparison with 15 占 폚) and the printing medium 110 in a time-wise manner. 8, at the time point S607 at which the print medium 110 passes through the color sensor 200 immediately after the toner image is fixed on the print medium 110, the temperature of the print medium 110 is about 65 占 폚. When the colorimetric value is measured at this point, a color difference (DELTA E76) of about 2.4 occurs for the color of the room temperature environment (15 to 30 DEG C) where the user uses the product. This means that the color difference (? E76) exceeds the color reproduction stability standard [4.2.3] (ΔE of each patch is less than 1.5).

In the present embodiment, the print medium 110 is caused to wait in the inverting unit 136 for a predetermined time T, and then conveyed back to the color sensor 200 to perform the colorimetric value measurement. At this time, the temperature of the print medium 110 is about 45 占 폚 or less. Therefore, in the present embodiment, the color difference? E76 can be reduced to less than 1.5 with respect to the colorimetric value measurement result at 15 占 폚 expected at the lowest temperature of the environment in which the image forming apparatus 100 is installed.

9 shows a possible temperature range of the print medium 110 for each kind of the print medium 110 in the image forming apparatus 100. As shown in Fig. In Fig. 9, the hatched range 901 represents an environment in which the operation of the image forming apparatus 100 is guaranteed. In the image forming apparatus 100 of the present embodiment, the temperature of the print medium 110 immediately after the patch image is fixed to the print medium 110 is 30 占 폚 to 70 占 폚. Therefore, when it is desired to set the color difference? E76 to 0.5 or less based on the minimum temperature (15 占 폚) of the installation environment, the predetermined time T is uniformly set to 45 seconds regardless of the type of the printing medium 110 It can be seen that it is enough to do.

In this embodiment, it is determined whether the air is necessary or unnecessary according to the type of the printing medium 110, and the predetermined time T is determined according to the type of the printing medium 110. [ In particular, by dynamically adjusting the predetermined time T according to the type of the print medium 110, the time taken for the colorimetric value measurement sequence can be minimized.

The heat capacity of the printing medium depends on its basis weight and the presence or absence of a surface coating material. If the heat capacity is different, the cooling time (predetermined time T) for cooling the print medium 110 to the target temperature is also different.

10 is a table showing the relationship between the predetermined time T, which is the cooling time, and the type of the print medium 110. According to Fig. 10, there are three kinds of surface properties, i.e. plain paper, single-sided coated paper and double-sided coated paper. In addition, three basic weights of 60 gsm to 109 gsm, 110 gsm to 209 gsm, and 210 gsm to 350 gsm are presented. In particular, the predetermined time (T) can be set to 0 only for plain paper without a surface coating layer. Using the table shown in Fig. 10, the printer controller 103 can set the predetermined time T as the minimum time according to the type of the print medium 110. [ That is, by dynamically controlling the predetermined time T, the time of the entire colorimetric value measurement sequence can be shortened. In this case, the table is stored in the storage unit 350 in advance.

As described above, according to the present embodiment, when the colorimetric value measurement is performed by the color sensor 200, the colorimetric value measurement is performed by the color sensor 200 from when the print medium 110 passes through the fusing unit Is set longer than the time taken for the print medium 110 to be conveyed from the fusing unit to the color sensor 200 when the colorimetric value measurement is not performed by the color sensor 200, , The colorimetric value is measured while the temperature of the print medium 110 is sufficiently lowered. Therefore, it is possible to stabilize the colorimetric value measurement result by the color sensor 200 even if the thickness, basis weight, and surface property of the print medium 110 are different. As a result,? E76 < 1.5 can be achieved.

[Example 2]

The present embodiment is characterized in that the colorimetric value is measured by the color sensor 200 after a predetermined time T without using the timer 310 in the engine control unit 102 of the image forming apparatus 100. [ Specifically, this embodiment will be useful in an image forming apparatus that does not have a standby position for waiting the print medium 110. [

(Image forming apparatus)

Hereinafter, the configuration of the image forming apparatus according to the present embodiment will be described. Fig. 11A shows an example in which the buffer unit 141 is provided inside the image forming apparatus 100, and Fig. 11B shows an example in which the buffer unit 141 is provided outside the image forming apparatus 100. Fig.

11A, the buffer portion 141 is disposed on the downstream side of the inverting portion 136 in the conveying direction of the print medium 110. In Fig. The engine control unit 102 switches the use / nonuse of the buffer unit 141 with the switching member 1101. [ The conveying speed in the buffer unit 141 is set such that the print medium 110 reaches the color sensor 200 after the temperature of the print medium 110 has sufficiently lowered. Is set to be slower than the conveying speed. It should be noted that instead of the conveying speed, the conveying distance of the buffer unit 141 may be designed to be long enough to sufficiently lower the temperature of the print medium 110. [

In Fig. 11B, the buffer unit 140 is connected to the downstream side of the image forming apparatus 100. Fig. The engine control unit 102 switches the use / nonuse of the buffer unit 141 with the switching member 1102. [ The conveying speed in the buffer unit 141 is set such that the print medium 110 reaches the color sensor 200 after the temperature of the print medium 110 has sufficiently lowered. Is set to be slower than the conveying speed. The post-processing unit 190 or the like can be connected to the downstream side of the buffer unit 140 in the conveying direction of the print medium 110. [ The post-processing unit 190 is a unit that performs punching, bookbinding, stapling, and the like. This buffer unit 140 also has an advantage that it can be added to an existing image forming apparatus.

The discharge path not passing through the buffer unit 141 is the first conveyance path in which the print medium 110 is guided when the colorimetric value measurement is not performed by the colorimetric value measurement unit. The discharge path via the buffer unit 141 is a second conveyance path in which the print medium 110 is guided when the colorimetric value measurement is performed by the colorimetric value measurement unit. 11A and 11B, the conveying distance of the second conveying path is longer than the conveying distance of the first conveying path. When the colorimetric value is not measured, the printer controller 103 controls the conveying roller, which is a conveying unit, to convey the printing medium 110 at the first conveying speed. When the colorimetric value measurement is performed, the printer controller 103 controls the conveying rollers to temporarily stop the printing medium, or to convey the printing medium at a second conveying speed that is slower than the first conveying speed. When the printing medium is temporarily stopped, the second conveying speed is reduced to zero, and the technical idea is common to the technical idea of the first embodiment.

In Fig. 11A, since the front and back of the print medium 110 are reversed when passing through the buffer unit 141, the color sensor 200 needs to be arranged on the opposite side as compared with Fig. Further, in order to measure the colorimetric value of the print medium 110 that does not need to pass through the buffer unit 141, it is necessary to arrange another color sensor 200 at the same position as in Fig. That is, two color sensors 200 are required. Of course, when the engine control unit 102 carries out the conveyance control so that the print medium 110 which does not need to pass through the buffer unit 141 also passes through the buffer unit 141, only one color sensor 200 suffices.

The buffer unit 140 shown in FIG. 11B may be useful when the buffer unit 141 can not be installed inside the housing 101 because of the size of the body of the image forming apparatus 100, as described above. It should be noted that the colorimetric value measurement sequence is basically common since the colorimetric values are measured after a predetermined time T elapses in Figs. 11A and 11B.

In the flowchart of Fig. 12, the same steps as those in the flowchart of Fig. 6 are given the same reference numerals, and a description thereof will be omitted. In Fig. 12, after steps S601 to S605 are executed, the process proceeds to step S1201. In step S1201, the printer controller 103 drives the switching member driving motor 313 through the engine control unit 102 to cause the switching member 132 to switch the conveying path, 135).

In step S1202, the printer controller 103 determines whether or not the type indicated by the print medium information requires a cooling time. This determination method is the same as that in step S610. For example, the printer controller 103 refers to a table stored in the storage unit 350 and determines whether or not the type is a type requiring a cooling time. The determination as to whether or not it is the kind requiring the cooling time is made substantially the same as whether it is necessary to guide the buffer unit 141 and whether or not it is necessary to lower the conveying speed of the printing medium in the buffer unit 141 Do. Therefore, this table is used to determine whether or not it is necessary to reduce the conveyance speed of the printing medium in the buffer unit 141 (the conveyance speed of the printing medium in the buffer unit 141) (I.e., whether or not the table is a table). As described above, the printer controller 103 acquires the conveyance path or conveyance speed corresponding to the print medium information received by the operation unit 180 from the table, and uses the obtained conveyance path or conveyance speed. If a cooling time is required, the process proceeds to step S1203. If no cooling time is required, the process advances to step S1204, and the printer controller 103 returns the print medium 110 to the color sensor 200. [

The printer controller 103 causes the switching member 1101 to switch the conveyance path through the engine control unit 102 and guides the print medium 110 to the buffer unit 141 in step S1203. The printer controller 103 activates the conveying roller driving motor 311 that drives the conveying roller disposed in the buffer unit 141 through the engine control unit 102 and controls the conveying roller driving motor 311 via the conveying path of the buffer unit 141 The print medium 110 is transported. The engine control unit 102 drives the conveying roller driving motor 311 such that the conveying speed of the printing medium 110 in the buffer unit 141 is slower than the conveying speed in the other conveying path such as the ejecting path 135 . Thus, the predetermined time T can be consumed and the temperature of the print medium 110 can be sufficiently lowered. It should be noted that it is not necessary to lower the conveying speed in the image forming apparatus capable of securing the conveying path in the buffer section 141 sufficiently long.

In step S1204, the printer controller 103 returns the print medium 110 returned to the discharge path 135 to the color sensor 200 again. Then, the process advances to step S614 to perform the colorimetric value measurement.

(Explanation of effect)

13 is a diagram showing the print medium waiting time, the print medium temperature,? E76 (comparison with 15 占 폚), and the print medium position (conveying distance) in a time-wise manner. At the time when the rear end of the printing medium 110 passes the switching member 1101, the engine control unit 102 lowers the conveying speed in the buffer unit 141 (step S1203). Thus, after the print medium 110 has left the fixing device and the predetermined time T has elapsed, the print medium 110 passes through the color sensor 200.

In the second embodiment, the temperature of the print medium 110 is about 65 占 폚 at the time when the print medium 110 first passes through the color sensor 200 as in the first embodiment. When the colorimetric value measurement is performed at this point, a color difference (? E76) of about 1.7 occurs for the color of the room temperature environment (25 占 폚) where the user uses the product. This value exceeds the color reproduction stability standard [4.2.3] (ΔE of each patch is less than 1.5).

In the present embodiment, the print medium 110 is guided to the buffer portion 141, and after the predetermined time T elapses, that is, after the temperature of the print medium 110 drops to 45 占 폚 or lower, Thereby allowing the medium 110 to reach the color sensor 200. Therefore, the color difference? E76 for the color of the expected minimum temperature (15 占 폚) of the environment in which the image forming apparatus 100 is installed can be reduced to 1.5.

[Example 3]

(Maximum concentration adjustment)

14 is a block diagram showing the system configuration of the image forming apparatus 100. As shown in Fig. First, the printer controller 103 instructs the engine control unit 102 to output a test chart used for adjusting the maximum density. At this time, a patch image for adjusting the maximum density of YMCK colors is formed on the printing medium 110 by the charging potential, the exposure intensity, and the developing bias set at the time of the preset maximum or previous density adjustment. Thereafter, the engine control unit 102 instructs the color sensor control unit 302 to measure the colorimetric value of the patch image.

After the colorimetric value of the patch image is measured by the color sensor 200, the colorimetric value measurement result is transmitted to the density conversion unit 324 as the spectral reflectance data. The density conversion unit 324 converts the spectral reflectance data into CMYK density data and transmits the converted density data to the maximum density correction unit 320. [

The maximum density correction unit 320 calculates the correction amount of the charging potential, the exposure intensity, and the developing bias so that the maximum density of the output image becomes a desired value, and transmits the calculated correction amount to the engine control unit 102. [ The engine control unit 102 uses the charge potential, the exposure intensity, and the correction amount of the developing bias transferred for the subsequent image forming operation. With the above-described operation, the maximum density of the output image is adjusted.

(Grayscale adjustment)

After the maximum density adjustment processing is completed, the printer controller 103 instructs the engine control unit 102 to form a 16-gradation patch image on the print medium 110. [ Note that the image signal of the 16-gradation patch image may be, for example, 00H, 10H, 20H, 30H, 40H, 50H, 60H, 70H, 80H, 90H, A0H, B0H, C0H, D0H, E0H and FFH do.

At this time, a 16-gradation patch image of YMCK colors is formed on the printing medium 110 by using the calculated charging potential, exposure intensity, and correction amount of the developing bias for the maximum density adjustment. When the 16-gradation patch image is formed on the print medium 110, the engine control unit 102 instructs the color sensor control unit 302 to measure the colorimetric value of the patch image.

After the colorimetric value of the patch image is measured by the color sensor 200, the colorimetric value measurement result is transmitted to the density conversion unit 324 as the spectral reflectance data. The density conversion unit 324 converts the spectral reflectance data into CMYK density data, and transmits the converted density data to the density tone correction unit 321. [ The density gradation correction section 321 calculates a correction amount of the exposure amount so as to acquire a desired gradation. The LUT generator 322 generates a monochrome gradation LUT and transmits the monochrome gradation LUT to the LUT unit 323 as the signal value of each CMYK color.

(Inter-sheet (patch) control)

The tone adjustment described above is not performed during a job because it takes time to control. Therefore, during the job, a patch image is formed at a time interval (interval) between the image on the intermediate transfer member 106 and the image, and the density change of the patch image is measured to control the density variation.

In this interspacing patch control, a patch image (40H in this embodiment) of a specific halftone density is formed on the intermediate transfer member 106 from among the patch images formed at the time of gradation adjustment described above, And is detected by the sensor 170. The density sensor 170 is driven by the density sensor control unit 328 based on an instruction from the engine control unit 102. [ The output signal of the density sensor 170 is transmitted to the density conversion unit 325.

The density conversion unit 325 converts the output signal from the density sensor 170 into CMYK density data. The LUT correction unit 326 corrects the monochromatic tone LUT set in the LUT unit 323 so that the density data is set to the target value T set in the target value storage unit 327. [ By controlling the image forming conditions in this manner, desired gradation characteristics can be obtained.

(Color characteristic of thermochromism)

Next, the color-by-color thermochromic characteristic will be described. As the molecular structure forming the coloring material such as toner or ink changes due to heat, the light reflection-absorption characteristic changes, and the chromaticity also changes. As a result of experiments, it was found that the tendency of chromaticity change was different for each color material as shown in Fig. The abscissa in this figure indicates the temperature of the patch image, and the ordinate indicates the chromaticity change? E with respect to the reference color at 15 占 폚.

DELTA E can be expressed as a three-dimensional distance between the two points ((L1, a1, b1), (L2, a2, b2)) in the L * a * b * .

15, C is 100% cyan, M is 100% magenta, Y is 100% yellow, K is 100% black, and W is paper white. As shown in this figure, the change in chromaticity of magenta is particularly large. As the temperature of the patch image becomes higher, the chromaticity change of the patch image becomes larger, and an error occurs in the generated ICC profile.

As an indicator of color matching accuracy and color stability, the ΔE average is specified as 4.0 in the color matching accuracy specification (IT8.7 / 4 (ISO12642: 1617 patch [4.2.2]) according to ISO 12647-7. In addition, reproducibility [4.2.3], which is a stability standard, stipulates that the ΔE of each patch is 1.5 or less. In order to satisfy such a condition, it is preferable that the detection accuracy of the color sensor 200 is? E? 1.0. As shown in Fig. 15, in order to realize? E? 1.0 with respect to the entire YMCK color, it is necessary to dissipate the heat of the patch image and reduce the temperature to 34 占 폚 or less.

(Relation between temperature and concentration value)

As described above, the chromaticity value (Lab value) changes with respect to the temperature. On the other hand, as a result of research conducted by the present applicant, it has been found that the concentration value does not substantially change even when temperature changes, and has no correlation with temperature. These results are shown in Fig.

The phenomenon that the chromaticity value changes when the temperature changes but the concentration value does not change can be explained from the difference between the region where the spectral reflectance changes and the calculation method of calculating the chromaticity value and the concentration value. With respect to this point, magenta (M) having a large chromaticity change DELTA E with respect to temperature change will be described as an example.

17 is the spectral reflectance data at each temperature acquired by measuring the colorimetric value of the magenta patch image with the color sensor 200. Fig. 17A is an enlarged view showing a whole wavelength range of 400 to 700 nm, FIG. 17B is an enlarged view showing a wavelength range of 550 to 650 nm, and FIG. 17C is an enlarged view showing a wavelength range of 500 to 580 nm.

As shown in Fig. 15, when the temperature of the patch image changes in the range of 15 占 폚 to 60 占 폚, the chromaticity change? E of magenta becomes about 2.0, and the chromaticity change? Because. It is difficult to understand the change of the spectral reflectance in Fig. 17A, but in Fig. 17B in which the wavelength range of 550 to 650 nm is enlarged, it is understood that the spectral reflectance changes due to the temperature change of the patch image. This is because the Lab operation unit 303 calculates the chromaticity by using the spectral reflectance in the entire wavelength range, and the chromaticity value changes due to the change of the spectral reflectance.

On the other hand, as shown in Fig. 16, even if the temperature of the patch image changes in the range of 15 占 폚 to 60 占 폚, the density does not substantially change. This is because the density converter 324 calculates the density using the spectral reflectance in a specific wavelength range. Specifically, the density conversion unit 324 converts the spectral reflectance data into density data using the filter shown in Fig. 18A for cyan, magenta, and yellow. In addition, the density converter 324 converts the spectral reflectance data into density data using the spectral characteristic of the time diagram as shown in Fig. 18B for black.

It can be seen that there is almost no change in the spectral reflectance in the wavelength region shown in Fig. 17C. 17C is a region having a sensitivity characteristic of green in the wavelength region indicated by the horizontal axis in Fig. 18A, and the density value of magenta is calculated using the sensitivity characteristic of green which is a complementary color of magenta. Therefore, since the spectral reflectance does not substantially change even if the temperature changes in this region, the concentration value does not substantially change.

As described above, the chromaticity of the patch image changes due to the temperature change, while the density of the patch image does not substantially change due to the temperature change. Therefore, in the present embodiment, the colorimetric value is measured by the color sensor 200 after releasing the print medium 110 heated by the fixing device at the time of multicolor correction (at the time of ICC profile creation). However, at the time of the maximum density adjustment and the tone adjustment, the colorimetric value of the print medium 110 is measured by the color sensor 200 without releasing the heat.

(Thermochromic technology)

Fig. 19 is a flowchart showing the operation of the image forming apparatus 100. Fig. This flowchart is executed by the printer controller 103. First, in step S1901, the printer controller 103 determines whether or not there is an image formation request by the operation unit 180 and whether or not there is an image formation request through the I / F 308 by the host computer.

If there is no image forming request, in step S1902, the printer controller 103 determines whether or not there is a multicolor correction instruction by the operation unit 180. [ If there is a multicolor correction instruction, the maximum density adjustment described later in Fig. 20 is performed in step S1903, and the gradation adjustment described later in Fig. 21 is performed in step S1904. Thereafter, in step S1905, the multi-color correction processing described later in Fig. 22 is performed. If there is no multicolor correction instruction in step S1902, the process returns to step S1901 described above. In this way, in order to accurately perform the multicolor correction processing, the maximum density adjustment and the tone adjustment are performed before the multicolor correction processing.

If it is determined in step S1901 that there is an image forming request, in step S1906, the printer controller 103 causes the container 113 to feed the print medium 110, and in step S1907, . Then, in step S1908, the printer controller 103 determines whether image formation is completed in the entire page. If the image formation is completed in the entire page, the process returns to step S 1901, and if not, the process returns to step S 1906, and image formation is performed on the next page. It should be noted that each time a predetermined number of image forming operations are performed, the above-described interspan patch control is performed to stabilize the density.

20 is a flowchart showing the maximum density adjustment operation. This flowchart is executed by the printer controller 103. It should be noted that the control of the image forming apparatus 100 is performed by the engine control unit 102 in response to the instruction from the printer controller 103. [

First, in step S2001, the printer controller 103 causes the print medium 110 to be fed from the container 113, and forms a patch image for adjusting the maximum density of YMCK colors on the print medium 110 in step S2002 . Next, in step S2003, the printer controller 103 causes the color sensor 200 to measure the patch image when the print medium 110 reaches the color sensor 200. Then,

In step S2004, the printer controller 103 causes the density conversion unit 324 to convert the spectral reflectance data output by the color sensor 200 into CMYK density data. Thereafter, in step S2005, the printer controller 103 calculates the charging potential, the exposure intensity, and the correction amount of the developing bias based on the converted density data. Here, the calculated correction amount is stored in the storage unit 350 and used.

21 is a flow chart showing the tone adjustment operation. This flowchart is executed by the printer controller 103. It should be noted that the control of the image forming apparatus 100 is performed by the engine control unit 102 in response to the instruction from the printer controller 103. [

First, in step S2101, the printer controller 103 causes the print medium 110 to be fed from the container 113. [ In step S2102, a patch image (16-gradation) for gradation adjustment of YMCK colors is formed on the print medium 110. [ Next, in step S2103, the printer controller 103 causes the color sensor 200 to measure the patch image when the print medium 110 reaches the color sensor 200. [

In step S2104, the printer controller 103 causes the density conversion unit 324 to convert the spectral reflectance data output by the color sensor 200 into CMYK density data. Thereafter, in step S2105, the printer controller 103 generates an LUT for correcting the gradation based on the converted density data. Here, the calculated LUT is set and used in the LUT unit 323.

22 is a flowchart showing the multicolor correction processing operation. This flowchart is executed by the printer controller 103. It should be noted that the control of the image forming apparatus 100 is performed by the engine control unit 102 in response to the instruction from the printer controller 103. [

First, in step S2201, the printer controller 103 causes the print medium 110 to be fed from the container 113. [ In step S2202, a patch image for multi-color correction processing is formed on the print medium 110. [ Then, in step S2203, the printer controller 103 detects that the print medium 110 reaches the reversing section 136 based on the detection of the trailing end of the print medium 110 by the reversing sensor 137 Until then, wait. In step S2204, when the print medium 110 reaches the inverting unit 136, the printer controller 103 controls the conveying roller driving motor 311 to stop conveying the print medium 110. [

When the conveyance of the print medium 110 is stopped in step S2204, in step S2205, the printer controller 103 performs a target value calculating process, which will be described later, with reference to Fig. This target value calculation processing is processing for calculating a target value T used in the above-described inter-base patch control. At this point, since both the maximum density adjustment and the tone adjustment were performed, the density of the output image was already adjusted to the desired density. Therefore, it is necessary to form a patch image on the intermediate transfer member 106 at this point and to set the density value of the patch image to the target value T in the span patch control.

After the target value calculation process is completed, in step S2206, the printer controller 103 determines whether or not a predetermined period of time (40 seconds in the present embodiment) has elapsed after the conveyance of the print medium 110 is stopped in step S2204 . Whether or not the predetermined time has elapsed is judged based on the count value of the timer started after the conveyance of the print medium 110 is stopped. Therefore, by stopping the conveyance of the print medium 110 for a predetermined time, the patch image of the print medium 110 is radiated. Therefore, the chromaticity change due to the influence of the thermochromism can be reduced.

As shown in Fig. 15, in order to realize? E? 1.0 with respect to the whole color of YMCK, it is necessary to dissipate the heat of the patch image and reduce the temperature to 34 占 폚 or lower. Here, the time required for heat radiation is set to 40 seconds in the present embodiment. When both the first fixing heater 342 installed in the first fixing device 150 and the second fixing heater 343 installed in the second fixing device 160 are used by stopping the printing medium 110 for 40 seconds The heat can be dissipated so that the Edo temperature is lowered to 34 占 폚 or less.

After the stop time of 40 seconds has elapsed, in step S2207, the printer controller 103 controls the conveying roller driving motor 311 to resume conveyance of the print medium 110. [ At this time, the printer controller 103 reverses the conveyance direction of the print medium 110 and conveys the print medium 110 toward the color sensor 200. [

When the print medium 110 reaches the color sensor 200, in step S2208, the printer controller 103 causes the color sensor 200 to measure the patch image. The printer controller 103 then calculates the chromaticity data (L * a * b *) from the spectral reflectance data output by the color sensor 200 using the Lab calculator 303. [ In step S2209, the printer controller 103 generates an ICC profile by the above-described processing based on the chromaticity data (L * a * b *). In step S2210, the ICC profile is stored in the output ICC profile storage unit 305. [

23 is a flowchart showing a target value calculation processing operation. This flowchart is executed by the printer controller 103. It should be noted that the control of the image forming apparatus 100 is performed by the engine control unit 102 in response to the instruction from the printer controller 103. [ The target value calculation process is performed during a period in which the conveyance of the print medium 110 is stopped and heat is released, as shown in Fig.

First, in step S2301, the printer controller 103 forms a patch image for background control on the intermediate transfer member 106. [ The signal value of the patch image formed here is 40H as described above. Then, in step S2302, the printer controller 103 measures the density of the patch image using the density sensor 170. [

In step S2303, the printer controller 103 calculates the density of the patch image as the target value T used in the interspan patch control. In step S2304, the target value T is stored in the target value storage unit 327. [ That is, in this flowchart, the output signal from the density sensor 170 for detecting the patch image is converted into YMCK density data, and the density data is stored in the target value storage unit 327 as the target value T.

In the interspacing patch control, the printer controller 103 compares the measured value of the patch image formed on the intermediate transfer member 106 during the continuous job with the target value T stored in the target value storage unit 327 in step S2304 , It should be noted that the LUT is corrected.

(Explanation of effect)

By performing the above-described control, the chromaticity change caused by the influence of the thermochromism can be reduced, the chromaticity of the patch image can be accurately detected, and the productivity can be improved. 24 compares the total time taken to perform both the maximum density adjustment, the tone adjustment, the multiple color correction processing, and the target value calculation processing in this embodiment and the comparative example. Note that in the comparative example, the target value calculation process is performed after the multicolor correction process is completed.

In the target value calculation processing for interspacing patch control, it takes about 30 seconds to form the patch image of the image signal 40H on the intermediate transfer member 106 and to measure the density of the patch image. In order to further improve the accuracy, a patch image may be formed and measured by using not only the target value T of the patch image of the image signal 40H but also other target values of the other image signals. In this case, Processing takes longer than 30 seconds.

As can be seen from Fig. 24, in the present embodiment, the target value calculation processing is performed during the multicolor correction processing, thereby shortening the total time by 30 seconds, that is, 20%.

As described above, in the present embodiment, during the execution of the multicolor correction process, until the colorimetric value measurement is performed by the color sensor 200 after the print medium 110 passes the fixing device, . Particularly, in this embodiment, while the conveyance of the print medium 110 is stopped and the patch image is being discharged, the target value calculation processing used in the interspan patch control is performed. Therefore, in this embodiment, the chromaticity change due to the influence of the thermochromism is reduced, the chromaticity of the measurement image can be accurately detected, and the productivity can be improved.

In the above description, the print medium 110 is temporarily stopped to stop the printing medium 110 until the colorimetric value is measured by the color sensor 200 after the print medium 110 passes the fixing device. . However, instead of temporarily stopping the printing medium 110, the colorimetric value measurement timing may be delayed by reducing the conveying speed of the printing medium 110. [

[Example 4]

(Thermochromic technology)

Fig. 25 is a flowchart showing the operation of the image forming apparatus 100. Fig. This flowchart is executed by the printer controller 103. First, in step S2501, the printer controller 103 determines whether there is an image formation request by the operation unit 180 and whether there is an image formation request via the I / F 308 by the host computer.

If there is no image formation request, in step S2502, the printer controller 103 determines whether or not there is a multicolor correction instruction by the operation unit 180. [ If there is a multiple color correction instruction, the multi-color correction process described later in Fig. 26 is performed in step S2503. If there is no multicolor correction instruction, the process returns to step S2501 described above.

If it is determined in step S2501 that there is an image forming request, the printer controller 103 causes the container 113 to feed the print medium 110 in step S2504. In step S2505, a toner image is formed on the print medium 110. [ Then, in step S2506, the printer controller 103 determines whether or not image formation is completed in the entire page. If image formation is completed in the entire page, the process returns to step S2501, and if not completed, the process returns to step S2504 to perform image formation on the next page.

26 is a flowchart showing the multicolor correction processing operation. This flowchart is executed by the printer controller 103. It should be noted that the control of the image forming apparatus 100 is performed by the engine control unit 102 in response to the instruction from the printer controller 103. [

First, in step S2601, the printer controller 103 causes the print medium 110 to be fed from the container 113. [ In step S2602, a patch image is formed on the print medium 110. [ Then, in step S2603, the printer controller 103 waits until the trailing end of the print medium 110 is detected by the reversing sensor 137. Then,

When the trailing end of the print medium 110 is detected by the reversing sensor 137, the printer controller 103 controls the conveying roller driving motor 311 to stop conveying the print medium 110 in step S2604. Then, in step S2605, the printer controller 103 waits until the time T elapses after the conveyance of the print medium 110 is stopped. Therefore, the patch image of the print medium 110 is dissipated while the print medium 110 is temporarily stopped by the inverting unit 136. [ Therefore, the chromaticity change due to the influence of the thermochromism can be reduced. The time T is set according to the setting of the basis weight, the surface property and the gloss of the print medium 110. This point will be described later in detail.

After the stop time T elapses, in step S2606, the printer controller 103 controls the conveying roller driving motor 311 to resume conveyance of the print medium 110. [ At this time, the printer controller 103 reverses the conveyance direction of the print medium 110 and conveys the print medium 110 toward the color sensor 200. [

When the print medium 110 reaches the color sensor 200, in step S2607, the printer controller 103 causes the color sensor 200 to measure the patch image. Thereafter, in step S2608, the printer controller 103 generates the ICC profile by the above-described processing based on the colorimetric value measurement result by the color sensor 200. [ In step S2609, the ICC profile is stored in the output ICC profile storage unit 305. [

(Setting the heat dissipation time)

The image forming apparatus 100 has seven fixing modes shown in Fig. The reason why the mode is provided in this manner is that it is necessary to change the fixing conditions according to the setting of the basis weight, the surface property and the glossiness of the print medium 110. [

27 is a view showing a print medium setting screen. 27A and 27B is displayed on the touch panel display provided on the operation unit 180. [ From the screen of Fig. 27A, the user selects which cassette in the container 113 to set. For example, when the cassette 1 is selected, the screen of Fig. 27B appears, and it becomes possible to set the basis weight, surface property and gloss of the print medium 110 stored in the cassette 1. Fig.

It is necessary to change the amount of heat necessary for fixing according to setting of basis weight, surface property and gloss of the printing medium 110. [ This is because the amount of heat absorbed by the printing medium 110 differs depending on the basis weight of the printing medium 110 when the toner image formed on the printing medium 110 is heated and fixed. In addition, when a large amount of heat is applied to a paper having a poor surface, such as a recycled paper, the toner deepens into the paper fiber to cope with the phenomenon that the quality is deteriorated. In addition, in order to meet the demand for user's glossiness, it is necessary to provide a plurality of fixing modes.

Fig. 29 shows the setting of the fixing mode in the case where the printing medium 110 is the recycled paper, Fig. 30 shows the setting of the fixing mode in the case where the printing medium 110 is high-quality paper, ) Is a coated paper, the setting of the fixing mode is shown. The engine control unit 102 controls the first fixing heater 342 provided in the first fixing device 150 and the second fixing device 160 installed in the second fixing device 160 according to the basis weight, And controls the heater 343.

As shown in Fig. 30, when the glossiness of the print medium 110 having a high quality paper sheet and a basis weight of 80 g / m2 is changed from "standard" to "-1 ", the glossiness of the first fixing device 150 The temperature is changed from 180 占 폚 to 165 占 폚. Also, for example, if the glossiness of "+1" is selected for the print medium 110 having a high quality paper sheet and a basis weight of 80 g / m 2, not only the first fixing device 150 but also the second fixing device 160 .

Therefore, if the fixing conditions are different, the temperature of the printing medium 110 when the colorimetric value is measured by the color sensor 200 is different. Therefore, it is necessary to set the waiting time T for stopping the printing medium 110 in the inversion unit 136 and releasing the heat in step S2605 in accordance with the basis weight, the surface property and the glossiness.

(1) the distance from the fixing device through which the print medium has last passed to the inverting portion 136, (2) the fixing temperature, and (3) the temperature of the printing medium 110 It is necessary to consider the heat radiation characteristic.

(1) The distance from the second fixing device 160 to the inverting portion 136 is shorter than the distance from the first fixing device 150 to the inverting portion 136. The printing medium 110 having passed both the first fixing device 150 and the second fixing device 160 reaches the reversing portion 136 more than the printing medium 110 having passed through only the first fixing device 150 The waiting time T in the reversing unit 136 is set to be long with respect to the former print medium 110 because the heat dissipation time is short.

(2) The higher the fixing temperature, the more the print medium 110 retains a large amount of heat. Therefore, it is necessary to set the waiting time T in the inverting unit 136 to be longer as the fixing temperature is higher.

(3) As the heat radiation characteristics of the print medium 110, heat is easily dissipated in the order of recycled paper, high-quality paper, and coated paper. Further, the smaller the basis weight of the print medium 110, the easier the heat dissipation.

In view of the above (1) to (3), the present applicant obtained an appropriate waiting time T in an experiment using the image forming apparatus 100. 32 shows the waiting time T in the inverting unit 136 in the case where the printing medium 110 is the recycled paper and FIG. 33 shows the waiting time T in the inverting unit 136 in the case where the printing medium 110 is the high- 34 shows the waiting time T in the inverting unit 136 when the print medium 110 is a coated paper.

As shown in FIGS. 32 to 34, the waiting time T is changed according to the setting of the basis weight, the surface property and the glossiness of the print medium 110, and the start time of the colorimetric value measurement by the color sensor 200 is changed do. Thus, the heat of the patch image can be dissipated until the colorimetric value measurement by the color sensor 200 is started, the temperature can be lowered to 34 占 폚, and? E? 1.0 can be realized.

As described above, in this embodiment, when the colorimetric value measurement is performed by the color sensor 200 from when the print medium 110 passes the fixing device based on the setting contents of the paper type of the print medium 110 Lt; / RTI &gt; Therefore, in this embodiment, the chromaticity change caused by the influence of the thermochromism is reduced, and the chromaticity of the patch image can be accurately detected.

Although the standby time T of the print medium 110 is optimized in the reversing unit 136 in this embodiment, the time from the passage of the print medium 110 through the fixing device to the arrival at the color sensor 200 The present invention is not limited to this configuration. For example, the time from when the print medium 110 passes the fixing device to when it reaches the color sensor 200 can be adjusted by decelerating the print medium 110 and controlling the deceleration time.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

The present application is based on Japanese Patent Application No. 2011-194414 filed on September 6, 2011, Japanese Patent Application No. 2011-226025 filed on October 13, 2011, and Japanese Patent Application No. 2011-226025 filed on October 5, 2011 Priority is claimed to Patent Application No. 2011-221233, which is incorporated herein by reference in its entirety.

Claims (20)

An image forming apparatus comprising:
Image forming means configured to form an image on a printing medium;
Fixing means configured to fix the image on the printing medium,
Conveying means configured to convey the printing medium along a conveying path and configured to reverse the conveying direction of the printing medium passing through the fixing means;
Color measuring means configured to measure a color of an image fixed on the printing medium at a downstream side of the fixing means in a conveying direction of the printing medium;
Wherein the edge of the print medium whose conveying direction is reversed from the time when the edge of the print medium passes through the fixing means when the color measuring means measures the color of the image fixed on the print medium, When the color measurement means does not measure the color of the image fixed on the print medium, the time from when the edge of the print medium passes through the fixing position to the time when the edge of the print medium passes through the fixing position, And control means configured to control the conveying means such that the edge of the print medium is longer than the time until the edge of the print medium passes through the measurement position of the color measuring means.
. The method according to claim 1,
Wherein when the color measuring means measures the color of the image fixed on the printing medium, the control means controls the printing means to stop the printing medium for a predetermined period of time, And controls to convey the medium,
. The method according to claim 1,
Wherein the control means controls the time from when the edge of the printing medium passes through the fixing means to when the edge of the printing medium passes the measuring position based on the type of the printing medium,
. The method according to claim 1,
Wherein the control means controls the conveying means to lower the conveying speed of the printing medium for a period of time after the printing medium passes the fixing means until the printing medium reaches the measurement position,
. The method according to claim 1,
Wherein the control means controls the fixing means such that the edge of the printing medium is moved from the position where the edge of the printing medium has passed the fixing means to the position of the measuring position on the basis of the fixing temperature used for fixing the image on the printing medium by the fixing means To the time when the vehicle passes through the vehicle,
. The method according to claim 1,
Wherein the conveying path includes a reversing portion,
Wherein the conveying means reverses the conveying direction of the printing medium by switching back the printing medium in the reversing direction,
. The method according to claim 1,
Conversion means configured to convert an image signal based on a conversion condition;
Further comprising updating means configured to update the conversion condition based on the measurement result of the image by the color measuring means,
Wherein the image forming means is further configured to form an output image based on the image signal converted by the converting means,
. The method according to claim 1,
Wherein the color measuring means comprises:
An irradiating means configured to irradiate an image with light;
A diffraction grating configured to disperse the light reflected by the image;
And a line sensor configured to receive light dispersed by the diffraction grating,
. 9. The method of claim 8,
Wherein the color measuring means is configured to measure the color of the image fixed on the print medium based on the intensity of the light received by the line sensor, the wavelength of which is in the range between 400 nm and 700 nm,
. The method according to claim 1,
Wherein said edge of said print medium is a leading end edge of said print medium in said conveying direction for a period of time during which said print medium is conveyed from said fixing means to said measuring position of said color measuring means,
. 3. The method of claim 2,
Wherein the predetermined time is a time at which a color difference (? E76) acquired by the color measuring means is 1.5 or less based on a temperature in an environment in which the image forming apparatus is installed,
. 3. The method of claim 2,
Wherein the predetermined time is a time at which the temperature of the print medium reaching the color measuring means decreases to 45 DEG C or less,
. 3. The method of claim 2,
Further comprising receiving means configured to receive print medium information indicating a thickness, a grammage, or a surface of the print medium,
Wherein a plurality of the predetermined times are defined for each piece of print medium information,
Wherein the control means determines the predetermined time corresponding to the print medium information received by the accepting means,
. The method according to claim 1,
Wherein the fixing means has a heater configured to heat an image to fix an image on the print medium,
. The method according to claim 1,
The image forming means is means for ejecting ink to form an image,
Wherein the fixing means is a drying means configured to dry the ink,
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